1. Field of the Invention
The present invention relates to a method and a system for scanning exposure, designed to expose a pattern formed in a mask on a substrate by moving the mask and the substrate in a predetermined direction in synchronization. Specifically, the invention relates to a method and a system for scanning exposure, designed to join and expose a plurality of divided patterns adjacent to each other on the substrate. The invention is based on Japanese Patent Applications Nos. 2000-25661 and 2000-26630, the contents of which are incorporated in the present invention.
2. Description of the Related Art
In recent years, as a display element for a personal computer, a television set or the like, liquid crystal display panels which can be made thin have been often used. The liquid crystal display panel of this kind is manufactured by patterning a transparent thin-film electrode in a desired shape on a rectangular photosensitive substrate when seen from above by a photolithographic method. As a photolithographic device for such a purpose, an exposure system has been used, which exposes a pattern formed on a mask (reticle) on a photoresist layer deposited on the photosensitive substrate through a projection optical system.
To enhance the case of viewing the screen, liquid crystal display panels have been greatly enlarged. For example, in the case of a panel for a personal computer, a large type having a size ranging from 307.34 mm (12.1 inch) to 358.14 mm (14.1 inch) has now become common. An example of an exposure system to meet such a demand was disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 7-57986. This is a scanning exposure system invented to sequentially transfer the patterns of a liquid crystal display (LCD) or the like formed on a mask in an exposure region on a glass substrate. The transfer is carried out by combining a plurality of projection optical systems for projecting mask patterns in erect images on the substrate, moving the mask and the glass substrate in a predetermined direction in synchronization, and scanning these with respect to each projection optical system, and a large exposure region is provided in a direction orthogonal to a synchronous moving direction.
In the described case, to obtain good image-forming characteristics without enlarging the exposure system even if the projection region is large, a device is used in which a plurality of projection optical systems are arranged such that projection regions adjacent to each other can be displaced by predetermined amounts in a scanning direction, and the end parts thereof can be overlapped in a direction orthogonal to the scanning direction. In this case, the field diaphragm of each projection optical system is, for example trapezoidal in shape, and the sum of the opening width of the field diaphragm in the scanning direction is set to be always equal. Accordingly, the described scanning exposure system is advantageous in that the joined parts of the projection optical systems adjacent to each other are exposed in overlapped fashion, and optical aberrations and the exposure illuminance of each projection optical system change smoothly.
With regard to a substrate used for manufacturing a liquid crystal display panel, in recent years, an idea has been presented to use a large glass substrate, one side thereof being equal to 50 to 70 cm or more, in order to achieve a higher productivity for simultaneous production of a number of liquid crystal display panels, and to manufacture a liquid crystal display panel having a larger display region for a television set or the like. To expose a substrate of a size equivalent to such a liquid crystal display panel having a large display region, there is a method of executing scanning exposure en bloc by using a mask having a size equal to the substrate size. Another method of dividing the pattern of one liquid crystal display panel into a plurality of regions and synthesizing these is available. The former method can provide high-speed throughput. Usually, however, because of the low pattern accuracy of the mask, it becomes prohibitively expensive to obtain a highly accurate mask for a so-called high-definition panel. Thus, this method lacks practicality.
On the other hand, the latter method needs to manage various errors including a reticle manufacturing error, resulting in complex correction work. In addition, when a correction error remains, it is difficult to obtain good picture synthesizing accuracy. For example, in a pattern joined part, a level difference may occur because of a mask pattern drawing error, the optical aberration of the projection optical system, the positioning error of a stage for moving the glass substrate, or the like, damaging the panel characteristics. Further, in the case of laminating synthesized patterns in multiple layers, the overlap error of the exposure regions of each layer, or pattern line errors discontinuously change in the pattern joined part, causing uneven coloring or the like in the joined part when the liquid crystal display panel is lit. Consequently, a reduction occurs in the quality of the panel.
To execute exposure on a large glass substrate while solving the foregoing problem, a scanning exposure system was disclosed, for example in Japanese Unexamined Patent Application, First Publication No. Hei 10-64782. This system is designed to join and transfer a plurality of divided patterns on a large glass substrate. Specifically, the operation is carried out by repeating, once or several times, a process including: executing scanning exposure by driving a mask stage for holding a mask and a substrate stage for holding the glass substrate in synchronization; then moving, stepwise, the mask stage and the substrate state in a direction orthogonal to the synchronous movement by a distance equivalent to the width of an irradiation region; partially overlapping a following exposure region with a preceding exposure region; and setting the exposure amount (exposing energy amount) of the overlapping part equal to that of a non-overlapping part.
Recently, however, demand for larger liquid crystal display panels has become stronger, requiring exposure on a much larger glass substrates. To meet such a request, a method of synthesizing pictures by joining divided patterns vertically and horizontally may be employed. Conventionally, however, in such a method the divided patterns cannot be joined smoothly in the scanning direction (synchronous moving direction). Thus, there is demand for a method of synthesizing pictures, which is capable of maintaining the device quality even when patterns are joined in the scanning direction as in the case of a non-scanning direction.
In addition, as described above, in the case of joining the divided patterns on the glass substrate by using one reticle, by changing the position of the glass substrate utilizing the characteristic of pattern repetition like the image pattern of a device pattern, exposure is carried out on a plurality of exposure regions while overlapping repetitive patterns among reticle patterns.
However, such image patterns are aligned at 0° or 90° (X or Y direction) to the device pattern. Also, the overlapping parts (picture synthesizing line) of the divided patterns on the glass substrate are frequently set along the 0° or 90° direction as in the case of image patterns. In the liquid crystal device, one problems in terms of display quality during picture synthesizing is an overlap accuracy difference in the process of manufacturing a driving transistor. This is mainly due to the fact that a control error of the driving transistor which causes the overlap accuracy difference between the left and right patterns across the picture synthesizing line, for example, exceeds the performance of the driving transistor and the minimum resolution of the gray scale decided upon by a used liquid crystal material.
Furthermore, if the extending direction of the picture synthesizing line is identical to the arraying direction of image patterns, driving transistors adjacent to the picture synthesizing line are all connected to the same gate line or signal line, and thus driven by the same timing. As a result, the effects of an overlap accuracy difference which is caused by the picture synthesizing on display quality are arranged on a straight line. Normally, if the locations of errors are scattered even when an error is large, the error is not so conspicuous. But the conspicuousness of errors is increased if the errors are arrayed in an orderly manner, even when the error is small. Consequently, if the effects of an overlapping accuracy difference are arranged on a straight line, then the display quality declines.
The present invention was made with the foregoing problems in mind, and the objects of the invention are to provide a method and a system for scanning exposure, capable of smoothly joining divided patterns adjacent to each other in a synchronous moving direction when picture synthesizing is carried out by moving a mask and a substrate in synchronization, and joining the patterns on the substrate. Furthermore, other objects of the invention are to provide a method and a system for scanning exposure, preventing an overlap accuracy difference caused by picture synthesizing from adversely affecting the display quality of a device.